This invention relates generally to roll mills for particle reduction including grinding and cracking of, for example, feed products. Two of the common problems associated with roll mills are the adjustment of the rolls relative to one another to effect the grinding or crushing of the particulate matter between the rolls and the drive means required for driving the two rolls simultaneously from a single power source at different speeds required for efficient particle reduction. In the past, this has been accomplished by either independent drives or cumbersome devices requiring additional adjustments with varying roll gaps.